Dual fuel injection valve and method of operating a dual fuel injection valve

ABSTRACT

A dual fuel injection valve separately and independently injects two different fuels and comprises a dual needle assembly with a hollow open-ended outer needle and an inner needle disposed within the hollow interior. A cap cooperates with the outer needle to cover the open end, and the outer needle and the cap together comprise the inner valve body. The outer and inner needles are each movable independently from each other between respective open and closed positions. A spring disposed between the cap and the inner needle contributes to biasing the inner needle in the closed position. The cap can be joined to the outer needle, whereby the cap can provide a limit to the movement of the inner needle. In another embodiment the cap can be detached from the outer body, allowing the spring to space the cap away from the outer needle, assisting with biasing the outer needle closed.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is a divisional of U.S. patent application Ser. No.09/989,623 filed Nov. 20, 2001 now U.S. Pat. No. 6,761,325, which is acontinuation-in-part of U.S. patent application Ser. No. 09/552,480filed Apr. 18, 2000 now U.S. Pat. No. 6,336,598, entitled “Gaseous andLiquid Fuel Injection Valve with a Two-Way Hydraulic Fluid ControlValve”, which is a continuation-in-part of U.S. patent application Ser.No. 09/154,103 filed Sep. 16, 1998, entitled “Gaseous and Liquid FuelInjection Valve”, now U.S. Pat. No. 6,073,862 issued Jun. 13, 2000. The'103 and the '480 applications are incorporated herein by reference intheir entirety.

FIELD OF THE INVENTION

The present invention relates to a hydraulically actuatable dual fuelinjection valve and a dual needle assembly, for injecting two differentfuels into the combustion chamber of an internal combustion engine.

BACKGROUND OF THE INVENTION

Because of its ready availability, low cost and potential for reducingparticulate emissions, natural gas is a promising substitute for dieselfuel for fuelling compression ignition engines, commonly known as“diesel-cycle” engines. Persons skilled in the technology involved herewill understand that natural gas is just one example of a preferredfuel, and that other fuels are also suitable, such as hydrogen, propaneand other fuels that are cleaner burning substitutes for diesel fuel. Acleaner burning substitute fuel for diesel is defined as a fuel that canbe used in an engine to substantially match the performance of adiesel-fuelled engine with lower particulate matter and/or nitrogenoxide (NOx) emissions.

Conventional methods of introducing a gaseous fuel into an engine premixall of the gaseous fuel with the intake air, which is a method known as“fumigation”. Engines using such an approach have been unable to matchthe power, performance, and efficiency of diesel-fuelled engines. Theapplicant has found that the inherent favorable operatingcharacteristics and high efficiency of conventional diesel-fuelledengines can be preserved when at least some of the gaseous fuel isintroduced directly into the engine's combustion chamber, late in thecompression stroke.

A problem with gaseous fuels such as natural gas is that, compared todiesel fuel, much higher temperatures and pressures are typically neededto auto-ignite the fuel. A solution to this problem, which allows thepreservation of the major components of diesel-cycle engines is toinject a small amount of more auto-ignitable fuel such as diesel fuel,to initiate the ignition and combustion of the cleaner burning gaseousfuel.

Using a pilot fuel in addition to a main charge of gaseous fuelpreferably requires the installation of at least two independentlyoperable injection valves, one for the pilot fuel and one for thegaseous main fuel. To avoid having to redesign and replace the cylinderhead, it is preferable to employ a gaseous and liquid fuel injectionvalve that fits into the same opening as a conventional diesel fuelinjection valve. Accordingly, there is a need for a gaseous and liquidfuel injection valve arrangement that allows independent introduction ofliquid pilot fuel and gaseous main fuel directly into the combustionchamber, and that has the same exterior dimensions as a conventionaldiesel injection valve.

SUMMARY OF THE INVENTION

A dual fuel injection valve separately injects a main fuel and a pilotfuel into a combustion chamber of an internal combustion engine. Thedual injection valve comprises:

-   -   (a) an injection valve body comprising:        -   a first-fuel inlet port through which a first fuel can be            introduced at injection pressure into the injection valve            body;        -   a first-fuel passage provided within the injection valve            body and extending between the first-fuel inlet port and a            first-fuel cavity;        -   a second-fuel inlet port through which a second fuel can be            introduced into the injection valve body;        -   a second-fuel passage connecting the second-fuel inlet port            to a second-fuel cavity; and        -   at least one first-fuel ejection port provided in the            injection valve body through which the first fuel can be            ejected directly into the combustion chamber from the            first-fuel cavity.    -   (b) a dual needle assembly comprising:        -   a hollow outer needle with an open end, wherein the outer            needle is movable within the injection valve body between a            closed position when a first sealing surface associated with            the outer needle is urged against a first seat associated            with the injection valve body near the first-fuel ejection            port thereby preventing the first fuel from flowing through            the first-fuel ejection port, and an open position when the            first sealing surface is spaced apart from the first seat            thereby allowing the first fuel to flow through the            first-fuel ejection port;        -   at least one second-fuel ejection port provided in the outer            needle through which the second-fuel can be ejected directly            into the combustion chamber from the second-fuel cavity;        -   an inner valve body comprising:            -   the outer needle; and            -   a cap associated with the open end of the outer needle;        -   an inner needle disposed within the inner valve body,            wherein the inner needle is movable within the inner valve            body between a closed position when a second sealing surface            associated with the inner needle is urged against a second            seat associated with the outer needle thereby preventing the            second fuel from flowing through the second-fuel ejection            port, and an open position when the second sealing surface            is spaced apart from the second seat, the cap providing a            surface facing the inner needle that limits the range of            movement for opening the inner needle; and        -   an inner spring disposed within the inner valve body between            the cap and the inner needle which contributes to biasing            the inner needle in the closed position;    -   (c) a first actuator assembly operable to selectively move the        inner needle between the open and closed positions; and    -   (d) a second actuator assembly operable to selectively move the        outer needle between the open and closed positions.

In preferred embodiments, the second-fuel cavity can be an annularvolume disposed between the inner needle and the outer needle, in whichthe inner needle has an outer diameter less than the inside diameter ofthe hollow outer needle.

The inner valve body can further define a hollow inner valve housingdisposed between the outer needle and the cap. In such embodiments, theinner valve housing can comprise a bore for housing the inner spring andthe space defined by the bore can be sealed from the second-fuel cavityby a match fit between the inner needle and the outer needle.

The cap can be joined in fixed relationship to the outer needle. Such anarrangement can facilitate manufacturing and assembly of the fuelinjection valve because the dual needle assembly can then be insertedinto the valve body as a single piece. With this embodiment it is alsopossible for the space defined by the bore of the inner valve housing tobe pressurizable with hydraulic fluid supplied from fluid passageswithin the injection valve body. In this way hydraulic fluid pressurecan be employed to provide an additional closing force to the innerneedle. The pieces of the inner valve body, including the cap, can bereleasably joined together by interlocking features. For example, theinterlocking features can be threaded joints. Alternatively, the innervalve body can comprise a plurality of separately made pieces that arepermanently joined together. For example, at least two of the pluralityof separately made pieces can be welded together.

In a preferred embodiment, at least one of the inner and outer valveneedles is hydraulically actuated and the injection valve body furthercomprises a hydraulic fluid inlet port, a hydraulic fluid drain port,and at least one control valve. Through the hydraulic fluid inlet port,pressurized hydraulic fluid can be introduced into fluid passages and acontrol chamber disposed within the interior of the injection valvebody. Through the hydraulic fluid drain port, hydraulic fluid can bedrained from the control chamber. At least one control valve that isoperable to selectively direct the flow of the hydraulic fluid andcontrol hydraulic fluid pressure within the control chamber to influencemovement of at least one of an outer needle and an inner needle betweenrespective open and closed positions.

A preferred embodiment of the disclosed fuel injection valve comprises:

-   -   (a) an injection valve body comprising:        -   a first-fuel inlet port through which a first fuel can be            introduced at injection pressure into the injection valve            body;        -   a first-fuel passage provided within the injection valve            body and extending between the first-fuel inlet port and a            first-fuel cavity;        -   a second-fuel inlet port through which a second fuel can be            introduced into the injection valve body;        -   a second-fuel passage connecting the second-fuel inlet port            to a second-fuel cavity;        -   at least one first-fuel ejection port provided in the            injection valve body through which the first fuel can be            ejected directly into the combustion chamber from the            first-fuel cavity;        -   a hydraulic fluid inlet port through which pressurized            hydraulic fluid can be introduced into fluid passages and a            control chamber disposed within the interior of the            injection valve body;        -   a hydraulic fluid drain port through which hydraulic fluid            can be drained from the control chamber; and        -   a control valve that is operable to selectively direct the            flow of the hydraulic fluid and control hydraulic fluid            pressure within the control chamber.    -   (b) a dual needle assembly comprising:        -   a hollow outer needle comprising an open end and an opposite            sealing end, which comprises a first sealing surface,            wherein the outer needle is movable within the injection            valve body between a closed position when the first sealing            surface is urged against a first seat associated with the            injection valve body near the first-fuel ejection port            thereby preventing the first fuel from flowing through the            first-fuel ejection port, and an open position when the            first sealing surface is spaced apart from the first seat            thereby allowing the first fuel to flow through the            first-fuel ejection port;        -   at least one fuel ejection port provided in the outer needle            through which the second fuel can be ejected directly into            the combustion chamber from the second-fuel cavity;        -   a cap associated with and detached from the open end of the            outer needle, wherein the cap is dynamically disposed within            the control chamber such that hydraulic fluid pressure            within the control chamber can apply a force that is            transmitted through the cap to the outer needle to influence            the position of the cap and outer needle;        -   an inner needle disposed within the outer needle, the inner            needle comprising a supported end opposite to a sealing end,            which comprises a second sealing surface, wherein the inner            needle is movable within the outer needle between a closed            position when the second sealing surface is urged against a            second seat associated with the outer needle thereby            preventing the second fuel from flowing through the            second-fuel ejection port, and an open position when the            second sealing surface is spaced apart from the second seat            thereby allowing the second fuel to flow through the            second-fuel ejection port; and        -   an inner spring disposed within the inner valve body between            the cap and the inner needle, whereby the inner spring            contributes to biasing the inner needle in the closed            position, and the inner spring can also contribute to            biasing the outer needle in the closed position by expanding            to space the cap away from the outer needle.

The supported end of the inner needle preferably has an outside diameterwhich is match fit with an inside diameter of a bore provided in theouter needle. The fuel injection valve can further comprise a memberthat supports one end of the inner spring and which transmits closingforces from the inner spring to the inner needle. By way of example, theinner spring can be a coil spring. The member can comprise a flange forreceiving one end of the coil spring and a stem which extends throughthe coil spring. The stem can cooperate with the cap to limit travel ofthe inner needle.

In preferred embodiments the volume of the control chamber is preferablyvariable in response to movement of the dual needle assembly. Pressurewithin the control chamber can be held at rail pressure to generate ahydraulic force that contributes to maintaining the outer needle in theclosed position. A spring preferably provides an additional closingforce that cooperates with the hydraulic force to maintain the outerneedle in the closed position. Fuel pressure within the first-fuelcavity preferably generates an opening force acting on the outer needlewhereby the outer needle is movable to the open position under theinfluence of the opening force when, by operation of the control valve,pressure within the control chamber is reduced to close to drainpressure.

In another embodiment, the outer needle is biased in the closed positionwhen pressure within the control chamber is at drain pressure or closeto drain pressure (that is, the control chamber pressure has a valuesufficiently near drain pressure such that the outer needle isnevertheless biased in the closed position) and the outer needle ismovable to the open position when hydraulic fluid pressure within thecontrol chamber is raised to rail pressure. In this embodiment, a springbiases the outer needle in the closed position so that when, byoperation of the control valve, hydraulic fluid pressure in the controlchamber is reduced to drain pressure the outer needle returns to theclosed position. The outer needle preferably comprises a shoulderdisposed within the first control chamber and when pressure within thefirst control chamber is raised to rail pressure the hydraulic force isapplied to the shoulder.

A method is provided of operating a fuel injection valve toindependently and separately inject two different fuels into acombustion chamber, wherein the fuel injection valve comprises a dualneedle assembly comprising an outer needle, a cap detachedly associatedwith an open end of the outer needle, an inner needle disposed andmovable within the outer needle, and an inner spring operativelyassociated with the inner needle and the cap. The method comprises:

-   -   moving the outer needle between a closed position where it is        seated against a first valve seat and an open position where it        is spaced apart from the first valve seat to regulate flow of a        first fuel into the combustion chamber through at least one        first fuel ejection port;    -   moving the inner needle between a closed position where it is        seated against a second valve seat and an open position where it        is spaced apart from the second valve seat to regulate flow of a        second fuel into the combustion chamber through at least one        second fuel ejection port;    -   controlling the movements of the outer and inner needles with        the movements of each needle being independent from the other;    -   pressurizing a control chamber associated with the outer needle        to apply a closing force to the outer needle, and reducing        pressure in the control chamber to drain pressure to allow the        outer needle to move to the open position; and    -   biasing the inner needle in the closed position with the inner        spring, which can also contribute to the closing force applied        to the outer needle by spacing the cap from the outer needle        when pressure in the control chamber is less than maximum        pressure and greater than drain pressure.

According to the method, the control chamber is pressurizable by beingfilled with a hydraulic fluid, and if the second fuel is a liquid fuel,the hydraulic fluid can be the second fuel.

The method can further comprise introducing the second fuel at injectionpressure into a second fuel cavity, where the second fuel applies anopening force to a shoulder surface of the inner needle.

Another embodiment of the method further comprises pressurizing a secondcontrol chamber associated with the inner needle to apply a closingforce to the inner needle in addition to the spring force of the innerneedle. In this embodiment the method comprises reducing pressure in thesecond control chamber to drain pressure to allow the inner needle tomove to the open position.

Yet another embodiment of the method further comprises increasing thepressure of the second fuel in a second fuel cavity to move the innerneedle to the open position, and reducing pressure in the second fuelcavity to cause the inner needle to move to the closed position.

In one embodiment, the first fuel is a main fuel and the second fuel isa pilot fuel that is more auto-ignitable than the main fuel. In apreferred embodiment, the first fuel is introduced into the first fuelcavity in the gaseous phase and the second fuel is introduced into thesecond fuel cavity in the liquid phase.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings illustrate specific embodiments of the invention, butshould not be considered as restricting the spirit or scope of theinvention in any way:

FIGS. 1 and 2 illustrate front and side elevation views of a dual fuelinjection valve.

FIGS. 3, 4 and 5 show respective detail, side and front section views ofa first embodiment of a dual fuel injection valve taken along sectionlines C—C, A—A, and B—B shown externally in FIGS. 1 and 2. Thisembodiment of the injection valve uses high-pressure hydraulic fluid tomaintain the first valve needle in the closed position.

FIGS. 6, 7 and 8 show respective detail, side and front section views ofa second embodiment of a dual fuel injection valve taken along sectionslines C—C, A—A, and B—B shown externally in FIGS. 1 and 2. Thisembodiment of the injection valve uses high-pressure hydraulic fluid tomove the first valve needle to the open position.

FIGS. 9 through 12 depict four different arrangements for an embodimentof an injection valve that is supplied with high pressure main fuel andpilot fuel at injection pressure where the respective injection valvesare each independently actuatable for separately injecting pilot fueland main fuel.

FIGS. 13 through 15 depict a preferred arrangement for a dual needleassembly for an injection valve. This embodiment of a dual needleassembly can be employed, for example, in an injection valve of the typedepicted in FIGS. 3 through 5. FIG. 13 is a side elevation view, FIG. 14is a section view, and FIG. 15 is an exploded view.

FIGS. 16 through 18 depict another preferred arrangement for a dualneedle assembly for an injection valve. This embodiment of a dual needleassembly can also be employed, for example, in an injection valve of thetype depicted in FIGS. 3 through 5. FIG. 16 is a side elevation view,FIG. 17 is a section view, and FIG. 18 is an exploded view.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT(S)

A dual fuel injection valve is capable of independently and separatelyinjecting a pilot fuel and a main fuel into a combustion chamber of aninternal combustion engine. That is, the injection valve providesindependent control of the injection timing and the fuel quantity forthe pilot fuel and main fuel. In addition, the pilot fuel and main fuelare injected into the combustion chamber separately, through differentejection ports.

The main fuel is a fuel that is cleaner burning than conventional dieselfuel such that substitution of the main fuel for diesel fuel results inlower emissions of particulate matter and/or nitrogen oxides (NOx)compared to an equivalent conventional engine that burns only dieselfuel. Preferably, on average, the main fuel comprises more than 90% ofthe fuel consumed by the engine measured on an energy basis.

In preferred embodiments, the main fuel is a gaseous fuel such asnatural gas, propane or hydrogen, and the pilot fuel is a liquid fuelsuch as diesel or dimethylether. The injection of the main fuel isindependent from the injection of the pilot fuel so that, for example,at least some of the gaseous fuel is injectable sequentially after theliquid fuel. The selected liquid fuel auto-ignites to promote combustionof the main fuel.

In the illustrated embodiments, the dual fuel injection valve isoperated using a constant high-pressure source of hydraulic fluid and atleast one electrically-operated electronically-controlled hydraulicfluid control valves. The control valve(s) control the flow of hydraulicfluid to manipulate at least one of two valve needles. A first valveneedle moves between an open and closed position for controlling theinjection of the main fuel into the combustion chamber. A second valveneedle moves between an open and closed position for controlling theinjection of the pilot fuel into the combustion chamber.

Referring to the drawings, FIGS. 1 and 2 show front and side elevationviews of an embodiment of a dual fuel injection valve. The exterior ofthe valve body can be shaped to fit the opening in the cylinder head inwhich it is to be installed. In this embodiment, twoelectrically-operated electronically-controlled hydraulic fluid controlvalves are used, one to control the injection of the main fuel and oneto control the injection of the pilot fuel. Specifically, FIG. 1 shows afront view of the exterior of dual fuel injection valve 1, with dualsolenoids 2 and 3 at one end and main fuel ejection ports 4 and pilotfuel ejection ports 5 at the opposite end. Solenoids 2 and 3electrically operate the hydraulic fluid control valves. Conventionalelectronic controls can be used to control the activation of solenoids 2and 3 to thereby control the timing and quantity of the injection eventswhereby the two different fuels are separately introduced into thecombustion chamber.

FIG. 2 illustrates a side view of dual fuel injection valve 1. In FIG.2, solenoid 3 is hidden behind solenoid 2.

Since the exterior of injection valve 1 as illustrated in FIGS. 1 and 2remains generally the same for the different internal embodiments, forpurposes of brevity, and to eliminate redundancy, FIGS. 1 and 2 are notrepeated.

With reference now to FIGS. 3 through 5, these Figures show respectivedetail, side, and front section views of a first embodiment of dual fuelinjection valve 1 taken along respective sections lines C—C, A—A, andB—B shown externally in FIGS. 1 and 2. This embodiment useshigh-pressure hydraulic fluid to bias main fuel valve needle 17 in theclosed position.

Injection valve 1 can comprise the following features for controllingthe flow of hydraulic fluid:

-   -   (a) three fluid inlets 6, 7, and 8;    -   (b) two drain ports 9 and 10;    -   (c) main fuel control solenoid 2;    -   (d) pilot fuel control solenoid 3;    -   (e) main fuel control valve 11;    -   (f) main fuel control valve spring 12;    -   (g) pilot fuel control valve 13; and    -   (h) pilot fuel control valve spring 14.

Preferably the hydraulic fluid and the pilot fuel are the same fluid andfluid inlets 6, 7 and 8 are all connected to a high pressure manifold,known as a “common rail” when the same manifold serves a plurality ofinjection valves in a multi-cylinder engine. Persons skilled in thetechnology involved here will understand that interior fluid passagescan be employed to reduce the number of fluid inlets and drain ports ina substantially equivalent structure.

A control valve for injection valve 1 controls the flow of hydraulicfluid into and out of the body of injection valve 1 by controllingwhether or not hydraulic fluid passages are fluidly connected to atleast one of inlets 7 and 8, or at least one of respective drain ports 9and 10. In the illustrated embodiment, valves 11 and 13 are two-wayvalves and are mechanically biased (by springs 12 and 14) in respectivepositions such that the hydraulic fluid passages that lead to respectivedrain ports 9 and 10 are blocked (as shown in FIG. 4). In thisembodiment, inlets 7 and 8 are always open, but flow is restricted byrespective orifices 7 a and 8 a. Other valve arrangements can beemployed for controlling the flow of hydraulic fluid. For example,instead of orifice 7 a or 8 a, injection valve 1 can employ a three-waycontrol valve such as, for example, a spool valve or a rotary valve,that alternately closes the respective inlet or outlet.

Injection valve 1 also preferably includes integral pilot fuelintensifier 15, which is illustrated in FIGS. 3 and 4. Intensifier 15 isfluidly linked to pilot fuel control valve 13.

As shown in FIG. 3, check valve 30 is associated with intensifier 15.Fluid passage 19, as seen in FIGS. 3 and 5, connects pilot fuel inlet 6to intensifier 15 through check valve 30. That is, check valve 30permits the one-way flow of pilot fuel from fluid passage 19 into space27 below intensifier 15.

Injection valve 1 has a dual fuel needle assembly that comprises twoconcentric needle valves. Outer needle 17 is a hollow body disposedaround inner needle 16. In preferred embodiments, outer needle 17controls the injection of one fuel into the combustion chamber and innerneedle 16 controls the injection of a second fuel into the combustionchamber.

The hollow body that is outer needle 17 also serves as the body for theinner needle valve assembly. The inner needle valve is in the closedposition when a sealing surface of inner needle 16 is urged against aseat that is provided by a sealing surface of outer needle 17. In theillustrated embodiment of FIGS. 3 through 5, inner needle 16 is biasedin the closed position by inner spring 18 in combination with thepressure of the hydraulic fluid within hydraulic fluid chamber 20.

A series of fuel ejection ports 4 are formed in the injection valve bodyat the tip of injection valve 1. A second series of fuel ejection ports5 are formed in the tip of outer needle 17. Ejection ports 4 and 5 andthe associated sealing surfaces of needles 16 and 17 are located at thetip of injection valve 1 to provide immediate injection of the main fueland pilot fuel into the engine combustion chamber (not shown).

Outer needle 17 preferably controls the injection of gaseous main fuelsince larger ejection ports are generally required for injecting largerquantities of main fuel compared to pilot fuel, and larger fuel ejectionports are more easily accommodated in the valve body rather than in thetip of outer needle 17. The smaller pilot fuel ejection ports can be canbe easily accommodated in tip of outer needle 17.

Main fuel control valve 11 controls the flow of hydraulic fluid fromchamber 20 to drain 10. When main fuel control valve 11 is in a closedposition, high pressure hydraulic fluid flows through inlet 8 andorifice 8 a and fills chamber 20. When main fuel control valve 11 isswitched to an open position, hydraulic fluid drains from chamber 20faster than it can be replenished through orifice 8 a. Consequently,when main fuel control valve is open, the pressure within chamber 20drops from the high pressure that is in the supply manifold (“railpressure”), to close to drain pressure and the pressure of the main fuelin chamber 22 applies an opening force to a shoulder area of outerneedle 17, causing outer needle 17 to retract within the injection valvebody so that fuel within chamber 22 flows into the combustion chamberthrough ejection ports 4.

Main fuel cavity 22 is located in the bottom region of injection valve 1and surrounds the lower portion of main fuel needle 17. The main fuel,which in preferred embodiments is gaseous fuel such as natural gas, issupplied to cavity 22 through inlet 23.

Differential pressures within injection valve 1 and particularly betweenmain fuel cavity 22 and the other cavities within the main body ofinjection valve 1 are preferably sealed by a fluid seal comprisinghydraulic fluid disposed within fluid seal cavity 24, as best seen inFIGS. 4 and 5.

Hydraulic fluid is supplied to the injection valve through a supplymanifold or common rail at a substantially constant pressure. Forexample, in vehicular applications, an engine driven pump can beemployed to pressurize the hydraulic fluid that is directed to thecommon rail. When the hydraulic fluid is different from the pilot fuel,the hydraulic fluid is introduced through ports 7 and 8 and the pilotfuel is introduced through inlet port 6. More preferably, the pilot fuelis a liquid fuel such as diesel, which can also be employed as thehydraulic fluid, and pilot fuel is supplied to ports 6, 7 and 8 from acommon pressurized system or common rail. The rail pressure is thepressure of the fluid in the common rail.

The operation of the injection valve illustrated in FIGS. 3 through 5 isdescribed herein for an embodiment that employs a gaseous fuel as themain fuel and a liquid fuel as the pilot fuel.

Inlet ports 7 and 8 are in constant fluid communication with respectivechambers 25 and 20. Between injection events, main fuel needle 17 andinner needle 16 are in the closed position where they prevent fluid flowthrough respective ejection ports 4 and 5. Main fuel control valve 11and pilot fuel control valve 13 are both in the closed position and thefluid pressure within chambers 25 and 20 is substantially equal to therail pressure of the hydraulic fluid that is introduced throughrespective ports 7 and 8. Pressurized pilot fuel flows through inletport 6 to fill space 27 below intensifier 15 via fluid passage 19 (seeFIG. 3). However, because the intensifier piston surface area facingchamber 25 is larger than the intensifier surface area facing space 27and the space between them is vented to drain, when second control valve13 is closed, intensifier 15 assumes a position that maximizes thevolume of chamber 25 and minimizes the volume of space 27 (as shown inFIGS. 3 and 4).

Inlet port 6 also supplies pressurized fluid to fluid seal cavity 24,where the pilot fuel provides a fluid seal around moveable outer needle17. When pilot fuel is used for sealing, the pilot fuel is pressurizedto a pressure equal to or slightly higher than that of the main gaseousfuel pressure within fuel cavity 22 to prevent the gaseous fuel fromleaking past fluid seal cavity 24 (see FIGS. 4 and 5). However, sealingfluid pressure is preferably controlled so that it is equal to or nottoo much greater than gaseous fuel pressure, since it is alsoundesirable for excessive amounts of sealing fluid to leak into fuelcavity 22.

Between injection events, when injection valve 1 is not injecting fuel,main fuel control solenoid 2 and pilot fuel control solenoid 3 (see FIG.4) are de-energized and control valves 11 and 13 are both biased in theclosed position by respective control valve springs 12 and 14. Thepressurized hydraulic fluid in chamber 20 that has been deliveredthrough port 8 maintains outer needle 17 in a closed position and canalso help to maintain inner needle 16 in a closed position. Thecompartment that houses inner spring 18 can be fluidly connected orsealed from chamber 20. When the spring compartment is fluidly connectedto chamber 20, the pressure within the compartment is about equal to thepressure in chamber 20. When the spring compartment is sealed fromchamber 20, the pressure within the compartment can be the same as thehydraulic fluid pressure at inlet 7 or at drain 9. Depending upon thefluid pressure within the spring compartment, some or all of the closingforce applied to inner needle 16 is provided by inner spring 18.

In the embodiments of FIGS. 3 through 6, the metering of pilot fuel byinjection valve 1 is accomplished by intensifier 15 that also serves toelevate the pressure of the pilot fuel to thereby open the inner needlevalve. When pilot fuel control valve 13 is opened, hydraulic fluidpressure within chamber 25 is reduced to drain pressure and the pressureof the pilot fuel in space 27 is sufficient to lift the intensifierplunger. When the desired amount of pilot fuel has been drawn into space27, pilot fuel control valve 13 is closed and hydraulic fluid pressurewithin chamber 25 is again elevated to a pressure close to railpressure. Under the influence of the high pressure hydraulic fluid inchamber 25, the intensifier plunger moves downward to compress andpressurize the pilot fuel in space 27. The elevated pressure of thepilot fuel ensures that check valve 30 remains closed and thepressurized pilot fuel is directed into the inner needle valve assemblythrough fluid passage 26; the pressurized pilot fuel causes inner needle16 to move to an open position against the bias imposed by inner spring18 and the fluid pressure within the spring compartment, if any. Innerneedle 16 returns to the closed position under the influence of innerspring 18 after the injection of pilot fuel into the combustion chamberrelieves the pressure of the pilot fuel within the inner needleassembly.

Inner spring 18 is disposed around inner needle stop 21, which islocated above inner needle 16. In the illustrated embodiments, innerneedle stop 21 includes a stem that limits the travel of inner needle16. While inner needle stop 21 is depicted as a separate piece frominner needle 16, inner needle stop 21 and inner needle 16 can also beintegrated into a single piece which would be functionally equivalent inlimiting the travel of inner needle 16. However, an additional advantageof employing two separate pieces is that it is easier to fabricate twopieces because portions of inner needle 16 are match-fit with outerneedle 17. As two separate pieces, inner needle stop 21 can functionwithout being perfectly aligned with inner needle 16 and dimensionalirregularities in the associated manufactured components can beaccommodated.

The injection of the main gaseous fuel takes place when the main fuelcontrol valve 11 opens to fluidly connect chamber 20 with drain port 10.The hydraulic fluid in chamber 20 drains through drain port 10 fasterthan it can be replenished from inlet port 8 through orifice 8 a.Consequently, the pressure in chamber 20 is reduced allowing the highpressure of the gaseous fuel in cavity 22 to lift main fuel needle 17into the open position to thereby inject the gaseous fuel within cavity22 into the engine combustion chamber through ejection ports 4. Theinjection of gaseous fuel stops when main fuel control valve 11 isclosed so that the pressure of the hydraulic fluid within chamber 20 isrestored to rail pressure, causing gaseous-fuel needle 17 to move to aclosed position, closing ejection ports 4.

FIGS. 6, 7, and 8 show respective detail, side, and front section viewsof a second embodiment of the double solenoid dual fuel injection valveshown externally in FIGS. 1 and 2, with the respective sections takenalong section lines C—C, A—A and B—B. This second embodiment has manycomponents that are equivalent to like components of the embodimentpresented in FIGS. 3, 4 and 5, and like components are identified bylike reference numbers. The main difference between the first and secondembodiments is that in the second embodiment outer spring 28 biasesouter needle 17 in the closed position and high pressure hydraulic fluidis used to move outer needle 17 to the open position opposed to thearrangement of the first embodiment which employs hydraulic fluidpressure to hold outer needle 17 in the closed position.

With reference to FIG. 7, high-pressure hydraulic fluid enters injectionvalve 1 through fluid inlet 8. Main fuel control valve 11 is a two-wayvalve that controls the hydraulic fluid pressure within fluid passage 29by controlling the flow of hydraulic fluid through drain port 10. Whentwo-way main fuel control valve 11 moves to its closed position, thefluid connection to drain port 10 is closed, causing the pressure incavity 29 b to increase. Rail pressure in cavity 29 b and the gaseousfuel pressure in cavity 22 combine to generate opening forces acting onouter needle 17 that are sufficient to overcome the closing force ofouter spring 28, thereby moving main fuel needle 17 to the openposition. The main fuel within cavity 22 is then injected throughejection ports 4, which are provided in the hollow tip of injectionvalve 1. An outer needle stop, similar to inner needle stop 21, limitsthe travel of outer needle 17 by limiting the compression of outerspring 28. The injection of gaseous fuel stops when main fuel controlvalve is opened and the hydraulic fluid pressure within cavity 29 b isreduced from rail pressure to drain pressure. Under the influence ofouter spring 28 outer needle 17 returns to the closed position with thesealing surface of needle 17 seated against a corresponding sealingsurface of the valve body.

The remaining features of the injection valve depicted in the secondembodiment function substantially the same as those described withreference to the first embodiment.

FIGS. 9 through 12 shows four different embodiments of anotherembodiment of a hydraulically actuated dual fuel injection valve forindependently and separately injecting a main fuel and a pilot fuel intoa combustion chamber. Each needle is associated with a respectivecontrol chamber in which the hydraulic fluid pressure can beindependently controlled to influence the movement of the respectiveneedle.

In the embodiments of FIGS. 9 and 10, high-pressure hydraulic fluidbiases both the outer needle and the inner needle in the closedposition. When hydraulic fluid pressure in a first control chamber isequal to rail pressure, the outer needle is held in the closed position,and when the pressure in the first control chamber is reduced to drainpressure, the outer needle moves to the open position under theinfluence of the fuel pressure acting on the outer needle. The hydraulicfluid pressure in a second control chamber is similarly controlled toinfluence the movement of the inner needle.

In the embodiments of FIGS. 11 and 12, the inner and outer needles arespring biased in the closed position and hydraulic fluid at railpressure directed to respective control chambers for the inner and outervalve needles to move them to the open position.

The pressure in the first and second control chambers is independentlycontrolled so that the movements of the outer needle and the innerneedle can be independent from one another.

With reference to all of the embodiments of FIGS. 9 through 12, likecomponents are identified by like reference numbers. In theseembodiments, injection valve 501 generally comprises the followingfeatures for controlling the flow of hydraulic fluid:

-   -   (a) at least one hydraulic fluid inlet such as 507 and/or 508;    -   (b) at least one drain port such as 509 and/or 510;    -   (c) main fuel hydraulic fluid control valve 511;    -   (d) pilot fuel hydraulic fluid control valve 513;    -   (e) main fuel control chamber 542; and    -   (f) pilot fuel control chamber 540.

Some of the features common to more than one embodiment will bedescribed in overview prior to describing the operation of eachembodiment.

In the embodiments illustrated in FIGS. 9 and 10, the pilot fuel and thehydraulic fluid can be different fluids and a separate pilot fuel inletport 506 is provided. However, if the pilot fuel and the hydraulic fluidare the same fluid a single common rail can be employed to supply fluidto the hydraulic fluid passages and to the fuel cavities within thepilot fuel valve assembly.

In the embodiments illustrated in FIGS. 11 and 12, the hydraulicactuation fluid for inner needle 516 and the pilot fuel are the samefluid, which avoids separate inlet ports for the pilot fuel and thehydraulic fluid for actuating the inner needle.

Main fuel hydraulic fluid control valves 511 and pilot fuel hydraulicfluid control valve 513 are generally the same as the hydraulic fluidcontrol valves described with reference to previously describedembodiments. That is, hydraulic fluid control valves 511 and 513 employa solenoid that is energized to move and hold the valve in one position.When the solenoid is de-energized, a spring moves and holds the valve inan opposite position. The operation of the injection valves will bedescribed in more detail below, but generally, different valve types canbe employed to control the flow of high pressure hydraulic fluid to andfrom control chambers 540 and 542. For example, FIGS. 9 and 11 showtwo-way valves for controlling hydraulic fluid flow and FIGS. 10 and 12show three way valves.

Like the embodiments of injection valve 1 shown in FIGS. 3 through 8,injection valve 501 has a dual fuel needle assembly that comprises twoconcentric needle valves. Outer needle 517 is a hollow body disposedaround inner needle 516. In preferred embodiments, outer needle 517controls the injection of a gaseous main fuel into the combustionchamber and inner needle 516 controls the injection of a liquid pilotfuel into the combustion chamber.

Inner needle stop 521 limits the travel of inner needle 516 and outerneedle stop 531 limits the travel of outer needle 517.

The hollow body that is outer needle 517 also serves as the body for theinner needle valve assembly. The inner needle valve is in the closedposition when a sealing surface of inner needle 516 is urged against aseat that is a sealing surface of outer needle 517.

A series of fuel ejection ports 504 are formed in the injection valvebody at the tip of injection valve 501. A second series of fuel ejectionports 505 are formed in the tip of outer needle 517, which provide anopening for ejecting the pilot fuel into the engine combustion chamberwhen the inner needle valve is in an open position. Ejection ports 504and 505 and the associated tips of needles 516 and 517 are locatedproximate to each other at the tip of injection valve 501 to provideimmediate injection of the main fuel and pilot fuel into the enginecombustion chamber (not shown).

Differential pressures within injection valve 501 and particularlybetween main fuel cavity 522 and the other cavities within the main bodyof injection valve 501 are preferably sealed by a fluid seal comprisinghydraulic fluid disposed within fluid seal cavity 524. In theembodiments of FIGS. 15 and 16, instead of a separate fluid seal cavity,the cavity employed for supplying liquid pilot fuel to the inner needleassembly can also serve as a fluid seal. This is convenientlyaccomplished when the pilot fuel supplied from the common rail to thepilot fuel cavity is already at injection pressure since this pressurecan be set to substantially match or slightly exceed the pressure of thegaseous fuel directed to main fuel cavity 522 through inlet 523. In theembodiments of FIGS. 11 and 12 a separate fluid seal cavity is employedbecause pilot fuel pressure is not always at rail pressure.

The operation of the different embodiments of injection valve 501illustrated in FIGS. 9 through 12 will be described below in relation toan injection valve that employs a gaseous fuel as the main fuel and aliquid pilot fuel as the pilot fuel.

In the embodiment of FIG. 9, when hydraulic fluid control valves 511 and513 are de-energized, these control valves are both spring-biased in theseated position to prevent hydraulic fluid from being drained fromrespective control chambers 542 and 540. Hydraulic fluid at railpressure is supplied to control chambers 542 and 540 through inlets 507and 508. The hydraulic fluid pressure within chambers 542 and 540 isthus normally maintained at rail pressure to apply a closing force torespective needles 517 and 516, in conjunction with the closing forcesapplied by springs 528 and 518.

When the solenoid for main fuel hydraulic fluid control valve 511 isenergized, this control valve opens and hydraulic fluid from main fuelcontrol chamber 542 drains through drain port 510 faster than it can bereplenished through inlet 508 because flow through inlet 508 isrestricted by orifice 508 a. Consequently, when main fuel hydraulicfluid control valve 511 is energized, the main fuel within main fuelcavity 522 is ejected from injection valve 501 through ejection ports504 because outer needle 517 moves to the open position under theinfluence of gaseous fuel pressure acting on shoulder 517 a whichovercomes the closing force of outer spring 528 and the drain pressurewithin control chamber 542. The main fuel injection event ends when thesolenoid is again de-energized and control chamber 542 is again filledwith hydraulic fluid at rail pressure.

In this embodiment, because the pilot fuel is supplied to injectionvalve 501 at injection pressure, there is no internal intensifier andinner needle 516 is operated in a manner very similar to outer needle517. When the solenoid for pilot fuel hydraulic fluid control valve 513is energized, this control valve opens and hydraulic fluid from pilotfuel control chamber 540 drains through drain port 509 faster than itcan be replenished through inlet 507 because flow through inlet 507 isrestricted by orifice 507 a. Consequently, when the solenoid for pilotfuel hydraulic fluid control valve 513 is energized, the pilot fuelwithin the inner needle assembly is ejected from injection valve 501through ejection ports 505 because inner needle 516 moves to the openposition under the influence of pilot fuel pressure acting on shoulder516 a which overcomes the closing force of inner spring 518 and thedrain pressure within control chamber 540. The pilot fuel injectionevent ends when the solenoid is again de-energized and control chamber540 is again filled with hydraulic fluid at rail pressure.

The embodiment of FIG. 10 operates in substantially the same way as theembodiment of FIG. 9 except that instead of employing two-way controlvalves with orifices to restrict flow through hydraulic fluid inlets 507and 508, the embodiment of FIG. 10 employs three-way control valvesemploying a spool-style valve to alternate between connecting controlchambers 540 and 542 with respective inlets 507 and 508 or drain ports509 and 510. In the illustrated embodiment, the spool valves are springbiased to connect control chambers 540 and 542 with respective inlets507 and 508. The needles 516 and 517 are thus normally in the closedposition because respective control chambers 540 and 542 are normallyfilled with hydraulic fluid at rail pressure. A main fuel or pilot fuelinjection event is initiated by energizing the solenoid for therespective hydraulic fluid control valve (513 for pilot fuel and 511 formain fuel). Energizing the solenoid moves the spool valve to a positionthat connects the respective control chamber with the drain port insteadof the inlet.

In the embodiment of FIG. 11, hydraulic fluid control valves 511 and 513are both spring-biased in the open position so that when theirrespective solenoids are de-energized, these control valves connect thehydraulic fluid passages and control chambers within injection valve 501with drain ports 509 and 510. That is, when the control valve solenoidsare de-energized, hydraulic fluid pressure within injection valve 501 isat drain pressure and inner spring 518 and outer spring 528 provide theforces needed to maintain inner needle 516 and outer needle 517 in theirrespective closed positions.

In the embodiment of FIG. 11, the pilot and the hydraulic fluid are thesame fluid and a pilot fuel injection event is initiated by energizingthe solenoid of pilot fuel hydraulic fluid control valve 513 to closedrain port 509 so that pilot fuel at rail pressure fills the fuel cavityof the inner needle assembly. The pilot fuel pressure exerts an openingforce on shoulder 516 a of inner needle 516 that overcomes the closingforce of inner spring 518, and pilot fuel is ejected from injectionvalve 501 through pilot fuel ejection ports 503. The pilot fuelinjection event is terminated de-energizing the solenoid to re-openpilot fuel hydraulic fluid control valve 513 so that pilot fuel pressurewithin the inner needle assembly is reduced to drain pressure, and innerspring 518 causes inner needle 516 to move to the closed position. Inthe illustrated embodiment, inner spring chamber 550 is not pressurizedand pilot fuel that migrates from the inner needle assembly to innerspring chamber 550 is recovered by being sent to the drain system.

A main fuel injection event in the embodiment of FIG. 11 is controlledin a similar manner to a pilot fuel injection event of the sameembodiment. By energizing the solenoid of main fuel hydraulic fluidcontrol valve 511 to close drain port 510, hydraulic fluid at railpressure fills control chamber 542 to exert an opening force on shoulder517 b of outer needle 517 which combines with the opening force exertedby the pressure of the gaseous fuel on shoulder 517 a to overcome theclosing force of outer spring 528. These opening forces cause outerneedle 517 to move to the open position to allow main fuel to be ejectedfrom injection valve 501 through main fuel ejection ports 504. The mainfuel injection event is terminated by re-opening main fuel hydraulicfluid control valve 511 so that hydraulic fluid pressure within controlchamber 542 is reduced to drain pressure, and outer spring 528 causesouter needle 517 to move to the closed position. In the illustratedembodiment, outer spring chamber 552 is not pressurized and hydraulicfluid that migrates from control chamber 542 to outer spring chamber 552is recovered by being sent to the drain system.

The embodiment of FIG. 12 operates in substantially the same way as theembodiment of FIG. 11 except that instead of employing two-way controlvalves with orifices to restrict flow through hydraulic fluid inlets 507and 508, the embodiment of FIG. 12 employs three-way control valvesemploying a spool-style valve to alternate between connecting needlevalve assemblies with respective inlets 507 and 508 or drain ports 509and 510. In the illustrated embodiment, the spool valves are springbiased to connect the pilot fuel and main fuel needle valve assemblieswith respective drain ports 509 and 510. The needles 516 and 517 arethus normally in the closed position because hydraulic fluid at railpressure is employed to open the needle valves. A main fuel or pilotfuel injection event is initiated by energizing the solenoid for therespective hydraulic fluid control valve (513 for pilot fuel and 511 formain fuel). Energizing the solenoid moves the spool valve to a positionthat connects the respective needle valve assembly with an inlet insteadof a drain port.

FIGS. 13 through 18 depict two different embodiments of a dual needleassembly that can be employed by an injection valve for independentlyinjecting two different fuels through separate ejection ports. Withreference to both embodiments illustrated in FIGS. 13 through 18, aninner spring provides the closing force that biases the inner needle inthe closed position, and hydraulic fluid pressure applied to the top ofthe dual needle assembly provides the closing force that biases theouter needle in the closed position.

With reference to FIGS. 13 through 15, dual needle valve assembly 600comprises outer needle 617 and cap 620. Tip 607 is the portion of theassembly that protrudes through an opening in the valve body as shown,for example, in FIG. 4. Pilot fuel ejection ports 605 are positioned onthe end of tip 607, as shown in FIG. 9.

Outer needle 617 features shoulder 610 that is disposable in a main fuelcavity such as main fuel cavity 22 shown in FIG. 4. The fuel pressure inthe main fuel cavity applies a hydraulic force to the shoulder area thatcauses outer needle 617 to move to the open position when the pressureabove cap 620 is reduced to drain pressure.

Because cap 620 is not attached to outer needle 617, inner spring 618can expand to space cap 620 away from outer needle 617. For example,when rail pressure is reduced but still higher than drain pressure,inner spring 618 can contribute to the closing force that keeps outerneedle 617 in the closed position. In this capacity inner spring 618advantageously provides additional benefits in addition to its primaryfunction of biasing inner needle 616 in the closed position.

Needle stop 621 comprises stem 621 b that limits the compression ofinner spring 618 when the end of stem 621 b is pressed against cap 620.Needle stop 621 further comprises flange 621 a which provides a seat forinner spring 618 so that the closing force applied by inner spring 618is transferred through needle stop 621 to inner needle 616 and the endof outer needle 617 when cap 620 is spaced apart from outer needle 617.

To reduce leakage, the portion of outer needle 617 between shoulder 610and the end facing cap 620 is match-fit with the valve body, as is theouter diameter of cap 620.

Pilot fuel port 615 provides a passage for supplying pilot fuel to theinner needle valve assembly. For example, with reference to FIG. 4, port615 would be aligned with the annular cavity that is supplied with fuelfrom intensifier 15 via fluid passage 26.

Those skilled in the technology involved here will understand that anouter spring and an outer needle stop can be added to the top of thedual needle assembly illustrated in FIGS. 13 through 15, for anembodiment suitable for use in an injection valve of the typeillustrated in FIGS. 6 through 8. In such an embodiment, outer needle617 further comprises an additional shoulder, located, for example,between pilot fuel port 615 and the end facing cap 620, which isassociated with a control chamber. Hydraulic fluid at rail pressure isdirectable to the control chamber to cause outer needle 617 to move tothe open position. When hydraulic fluid pressure in the control chamberis reduced to drain pressure, the outer spring exerts a closing force onouter needle 617 that moves it to the closed position. In thisembodiment, cap 620 can be attached to outer needle 617, for example, bya threaded connection, since in such an embodiment inner spring 618 doesnot add to the closing force of the outer spring.

Another embodiment of the dual needle assembly is depicted in FIGS. 16through 18. Dual needle assembly 700 comprises an inner needle assemblythat is similar to that of the previously described embodiments. Thatis, inner needle 716 is biased in the closed position by inner spring718 that transmits a closing force through the flange of inner needlestop 721. Inner needle 716 is disposed within hollow outer needle 717and a sealing surface near the tip of inner needle 716 seats against asealing surface of outer needle 717 when in the closed position. Highpressure pilot fuel is directed to pilot fuel port 715 to move innerneedle 716 to an open position.

The inner needle assembly is housed within the hollow body of outerneedle 717, inner valve housing 730, and inner valve cap 722, which areall releasably joined to each other in a fixed relationship, forexample, by threaded connections. Inner valve cap 722 and inner valvehousing 730 could also be integrated as a single component if thearrangement is modified to allow inner spring 718 and inner needle stop721 to be inserted from the bottom. The inner spring chamber, whichhouses inner spring 718 can be connected by port 732 to the hydraulicfluid system at rail pressure or drain pressure, or to the pressurizedpilot fuel supply system. That is, the inner spring chamber need not bepressurized, but an advantage of filling this chamber with pressurizedfluid is that the fluid pressure acts upon the flange of inner needlestop 721 to contribute to the closing forces applied to inner needle 716so that a smaller inner spring can be employed.

Plunger 720 is match fit with the valve body with the top of plunger 720forming one of the boundaries for a hydraulic fluid chamber such aschamber 20 shown in FIGS. 4 and 5. When the hydraulic fluid chamber isfilled with hydraulic fluid at rail pressure, outer needle 717 is heldin the closed position by a closing force that is transmitted to itthrough plunger 720, inner valve cap 722, and inner valve housing 730.When the hydraulic fluid chamber is connected to a drain port and thepressure is reduced to drain pressure, the high pressure fuel acts onshoulder 710 to move outer needle 717 to the open position.

Outer spring 724 is disposed between inner valve cap 722 and seatingring 726 that is itself seated against a fixed annular ledge of thevalve body. Outer spring 724 contributes to the closing force for outerneedle 717 to keep it in the closed position when rail pressure isreduced but still higher than drain pressure. Outer spring 724 alsohelps to shape the injection pulse by slowing the outer needle rise timeand accelerating the outer needle closing.

Tip 707 is the portion of the assembly which passes through an openingin the valve body as shown, for example in FIG. 4. Pilot fuel ejectionports 705 are positioned on the end of tip 707, as shown in FIG. 12.

To reduce leakage, the portion of outer needle 717 between shoulder 710and the end joined to inner valve housing 730 is match-fit with thevalve body.

As will be apparent to those skilled on the art in the light of theforegoing disclosure, many alterations and modifications are possible inthe practice of this invention without departing from the scope thereof.Accordingly, the scope of the invention is to be construed in accordancewith the substance defined by the following claims.

1. A dual fuel injection valve operable to independently and separatelyinject two different fuels into a combustion chamber of an internalcombustion engine, said dual fuel injection valve comprising: (a) aninjection valve body comprising: a first-fuel inlet port through which afirst fuel can be introduced at injection pressure into said injectionvalve body; a first-fuel passage provided within said injection valvebody and extending between said first-fuel inlet port and a first-fuelcavity; a second-fuel inlet port through which a second fuel can beintroduced into said injection valve body; a second-fuel passageconnecting said second-fuel inlet port to a second-fuel cavity; at leastone first-fuel ejection port provided in said injection valve bodythrough which said first fuel can be ejected directly into saidcombustion chamber from said first-fuel cavity; (b) a dual needleassembly comprising: a hollow outer needle with an open end, whereinsaid outer needle is movable within said injection valve body between aclosed position when a first sealing surface associated with said outerneedle is urged against a first seat associated with said injectionvalve body near said first-fuel ejection port thereby preventing saidfirst fuel from flowing through said first-fuel ejection port, and anopen position when said first sealing surface is spaced apart from saidfirst seat thereby allowing said first fuel to flow through saidfirst-fuel ejection port; at least one second-fuel ejection portprovided in said outer needle through which said second-fuel can beejected directly into said combustion chamber from said second-fuelcavity; an inner valve body comprising: said outer needle; and a capassociated with said open end of said outer needle; an inner needledisposed within said inner valve body, wherein said inner needle ismovable within said inner valve body between a closed position when asecond sealing surface associated with said inner needle is urgedagainst a second seat associated with said outer needle therebypreventing said second fuel from flowing through said second-fuelejection port, and an open position when said second sealing surface isspaced apart from said second seat, said cap providing a surface facingsaid inner needle that limits the range of movement for opening saidinner needle; and an inner spring disposed within said inner valve bodybetween said cap and said inner needle which contributes to biasing saidinner needle in said closed position; (c) a first actuator assemblyoperable to selectively move said inner needle between said open andclosed positions; and (d) a second actuator assembly operable toselectively move said outer needle between said open and closedpositions.
 2. The dual fuel injection valve of claim 1 wherein saidsecond-fuel cavity is an annular volume disposed between said innerneedle and said outer needle wherein said inner needle has an outerdiameter less than the inside diameter of said hollow outer needle. 3.The dual fuel injection valve of claim 1 wherein said inner valve bodyfurther comprises a hollow inner valve housing disposed between saidouter needle and said cap, wherein said inner valve housing comprises abore for housing said inner spring and the space defined by said bore issealed from said second-fuel cavity by a match fit between said innerneedle and said outer needle.
 4. The dual fuel injection valve of claim3 wherein said cap is joined in fixed relationship to said outer needle.5. The dual fuel injection valve of claim 4 wherein the space defined bysaid bore of said inner valve housing is pressurizable with hydraulicfluid supplied from fluid passages within said injection valve body. 6.The dual fuel injection valve of claim 4 wherein pieces of said innervalve body are releasably joined together by interlocking features. 7.The dual fuel injection valve of claim 6 wherein said interlockingfeatures are threaded joints.
 8. The dual fuel injection valve of claim1 wherein said inner valve body comprises a plurality of separately madepieces that are permanently joined together.
 9. The dual fuel injectionvalve of claim 8 wherein said at least two of said permanently joinedpieces are welded together.
 10. The dual fuel injection valve of claim 1wherein said injection valve body further comprises: a hydraulic fluidinlet port through which pressurized hydraulic fluid can be introducedinto fluid passages and a control chamber disposed within the interiorof said injection valve body; a hydraulic fluid drain port through whichhydraulic fluid can be drained from said control chamber; and at leastone control valve that is operable to selectively direct the flow of thehydraulic fluid and control hydraulic fluid pressure within said controlchamber to influence movement of at least one of an outer needle and aninner needle between respective open and closed positions.
 11. A fuelinjection valve operable to independently and separately inject twodifferent fuels into a combustion chamber, said fuel injection valvecomprising: (a) an injection valve body comprising: a first-fuel inletport through which a first fuel can be introduced at injection pressureinto said injection valve body; a first-fuel passage provided withinsaid injection valve body and extending between said first-fuel inletport and a first-fuel cavity; a second-fuel inlet port through which asecond fuel can be introduced into said injection valve body; asecond-fuel passage connecting said second-fuel inlet port to asecond-fuel cavity; at least one first-fuel ejection port provided insaid injection valve body through which said first fuel can be ejecteddirectly into said combustion chamber from said first-fuel cavity; ahydraulic fluid inlet port through which pressurized hydraulic fluid canbe introduced into fluid passages and a control chamber disposed withinthe interior of said injection valve body; a hydraulic fluid drain portthrough which hydraulic fluid can be drained from said control chamber;and a control valve that is operable to selectively direct the flow ofthe hydraulic fluid and control hydraulic fluid pressure within saidcontrol chamber; (b) a dual needle assembly comprising: a hollow outerneedle comprising an open end and an opposite sealing end, whichcomprises a first sealing surface, wherein said outer needle is movablewithin said injection valve body between a closed position when saidfirst sealing surface is urged against a first seat associated with saidinjection valve body near said first-fuel ejection port therebypreventing said first fuel from flowing through said first-fuel ejectionport, and an open position when said first sealing surface is spacedapart from said first seat thereby allowing said first fuel to flowthrough said first-fuel ejection port; at least one fuel ejection portprovided in said outer needle through which said second fuel can beejected directly into said combustion chamber from said second-fuelcavity; a cap associated with and detached from said open end of saidouter needle, wherein said cap can be dynamically disposed within saidcontrol chamber such that hydraulic fluid pressure within said controlchamber can apply a force that is transmitted through said cap to saidouter needle to influence the position of said cap and outer needle; aninner needle disposed within said outer needle, said inner needlecomprising a supported end opposite to a sealing end, which comprises asecond sealing surface, wherein said inner needle is movable within saidouter needle between a closed position when said second sealing surfaceis urged against a second seat associated with said outer needle therebypreventing said second fuel from flowing through said second-fuelejection port, and an open position when said second sealing surface isspaced apart from said second seat thereby allowing said second fuel toflow through said second-fuel ejection port; and an inner springdisposed within said inner valve body between said cap and said innerneedle, whereby said inner spring contributes to biasing said innerneedle in said closed position, and said inner spring can alsocontribute to biasing said outer needle in said closed position byexpanding to space said cap away from said outer needle.
 12. The dualfuel injection valve of claim 11 wherein said supported end of saidinner needle has an outside diameter which is match fit with an insidediameter of a bore provided in said outer needle.
 13. The fuel injectionvalve of claim 12 further comprising a member that supports one end ofsaid inner spring and which transmits closing forces from said innerspring to said inner needle.
 14. The fuel injection valve of claim 13wherein said spring is a coil spring.
 15. The fuel injection valve ofclaim 14 wherein said member comprises a flange for receiving one end ofsaid coil spring and a stem which extends through said coil spring,whereby said stem cooperates with said cap to limit travel of said innerneedle.
 16. A method of operating a fuel injection valve toindependently and separately inject two different fuels into acombustion chamber, wherein said fuel injection valve comprises a dualneedle assembly comprising an outer needle, a cap detachedly associatedwith an open end of said outer needle, an inner needle disposed andmovable within said outer needle, and an inner spring operativelyassociated with said inner needle and said cap, said method comprising:moving said outer needle between a closed position where it is seatedagainst a first valve seat and an open position where it is spaced apartfrom said first valve seat to regulate flow of a first fuel into saidcombustion chamber through at least one first fuel ejection port; movingsaid inner needle between a closed position where it is seated against asecond valve seat and an open position where it is spaced apart fromsaid second valve seat to regulate flow of a second fuel into saidcombustion chamber through at least one second fuel ejection port;controlling the movements of said outer and inner needles with themovements of each needle being independent from the other; pressurizinga control chamber associated with said outer needle to apply a closingforce to said outer needle, and reducing pressure in said controlchamber to drain pressure to allow said outer needle to move to saidopen position; and biasing said inner needle in said closed positionwith said inner spring, which can also contribute to the closing forceapplied to said outer needle by spacing said cap from said outer needlewhen pressure in said control chamber is less than maximum pressure andgreater than drain pressure.
 17. The method of claim 16 wherein saidcontrol chamber is pressurizable by being filled with a hydraulic fluid.18. The method of claim 17 wherein said hydraulic fluid is said secondfuel.
 19. The method of claim 16 further comprising introducing saidsecond fuel at injection pressure into a second fuel cavity, where saidsecond fuel applies an opening force to a shoulder surface of said innerneedle.
 20. The method of claim 19 further comprising pressurizing asecond control chamber associated with said inner needle to apply aclosing force to said inner needle in addition to the spring force ofsaid inner needle, and reducing pressure in said second control chamberto drain pressure to allow said inner needle to move to said openposition.
 21. The method of claim 16 further comprising increasing thepressure of said second fuel in a second fuel cavity to move said innerneedle to said open position, and reducing pressure in said second fuelcavity to cause said inner needle to move to said closed position. 22.The method of claim 16 further comprising introducing said first fuelinto said first fuel cavity in the gaseous phase, and introducing saidsecond fuel into said second fuel cavity in the liquid phase.
 23. Themethod of claim 16 wherein said second fuel is a liquid pilot fuel thatauto-ignites more readily than said first fuel.